Molding mixture



.April 9, 1929. L.. M. HULL HOLDING MIXTURE Original Filed Sept. 1, 1925 Patented pr. .9, 1929,

UNITED STATES PATENT OFFICE.

LEWIS MQ HULL, OF BOONTON, NEW JERSEY, ASSIG-NOR TO RADIO FREQUENCY LAB- f. ORATORIES INCORPORATED, OF BOONTON, NEW JERSEY, A CORPORATION OF NEW JERSE.

HOLDING MIXTURE.

Continuation of application Serial No. 53,947, led September 1, 1925. This application led June 30, 1926. Serial No. 119,570.

This invention relates to molding mixtures of the known type having a binder consist-ing wholly or in part of a reactive phenolic-resin, admixed with an inert filler, and

to molded articles made therefrom. A primary object of the invention is to provide such a mixture which, when subjected to pressure-molding with coincident, or in some cases with subsequent, heat-ing will yield a molded product possessing inY full measure the well-known advantages and desirable qualities of the commercial phenol-resin molded articles, such for example as those in which the filling material is wood-Hour h mechanical strength, good molding qua ity, excellent surface characteristics coupled with faithful reproduction of the mold, permanence as against the action of.

moisture and ordinary temperature changes,

.. etc.) and in addition theretofhaving at all frequencies (including radio frequencies) a Vdistinctly lower dielectric hysteresis than that which characterizes the said commercial molded articles as heretofore produced. Rep- 26 -resentative phase difference values for these commercial molded articles lie between 1.5 and 4.0 degrees, corresponding to a power factor of about 2.6 to 7.0% (compare Technologic Paper of the Bureau of Standards,

30 No. 216, page 622).v My investigations of a series of specially compounded mixtures, comprising various reactive phenol resins with commercial lillers, have shown that the dielectric h steresis in the molded article increases as a ru e rather rapidly with the proportion of filler used, clearly indicating that the relatively high hysteresis characterizingV certain commercial products of this type is attributable rather to the filler used than to the resin component. This indicated the possibility, at least, of

preparing a mixture which would yield a.

molded article of low dielectric hysteresis, approximatinv for example that of hard rubber; and my further investigations have resulted in the development of such mixtures,-

. combining excellent electrical properties with satisfactory mechanical and molding qualities, as hereinbelow explained.

resin will, on suflicient application ofheat,

become transformed to the infusible or resinoid modification. I have ascertained that some of these phenolic resins, in the absence of any filler, will yield a hardened product of low dielectric hysteresis, and I use such low hysteresis resins for the purpose of this invention. The suitability of any particular resin may thus be determined by simple and direct test, resins having a phase angle difference of 1.00,- or lower, when measured ata wave-length of 300 meters, being preferably selected. Phenolic resins having a phase an-` gle difference of 0.66 and 0.71o are now available.

As a filler form novel molding composition I may suitab y employ an inert solid which-possesses the two qualities of low inherent phase angle difference, and of remaining unchanged and non-reactive as regards the other ingredients,'during the process of molding. Examples of such solids, which I have experimentally determined to be sat-isfactory, are mica and silica, and powdered vitreous materials such as glass and quartz'. Either of these substances may be used alone,

'ora mixture may be employed. I have found ymica to be somewhat preferable to silica as regards the molding qualities of the resulting mixture, although the dielectric ualities are satisfactory in both cases. Whi e vpowdered hard-rubber possesses a low phase anle difference, I have found that it is subject to suchC change during the molding process that the phase angle difference of the resulting molded dielectric may be very high.

therefore, an example of an unsuitable A satisfactory mixture may be compounded from the ingredients described above. In certaln cases, however, 1t may be deslred to 1ncrease the tensile strength of the final product.

To this end a fibrous or cellulosic material may be added to the molding mixture, and the criterion for the selection of such a fibrous material 'is that it must not too far detract from the .-'dielectric qualities of the mixture resultin from the resin and inert filler alone. I have ound silk, cotton, and other fibrous or cellulosic materials to be satisfactory forv If silk is employed a satis-- factory grade is raw Chinese silk whichv has this purpose.

not been boiled off. Cotton which is vcarefully dried, as by baking or otherwise, may be substituted for silk at only a slight sacrifice of dielectric quality. I have found that as much as say of silk maybe used without undul increasing the phase angle difference o the resulting product. Ctton, however, must be used in quantities not exceeding say 3% if the phase difference of the molded -productis4 to remain below 1.0. Other fibrous or cellulosic materials may be employed in a similar manner, and in such c ase the proportions are to be regulated so as not unduly to increase the phase angle difference. For producing small or complicated molded parts from myinvention the fibrous material, if used, is preferably runthrough a cuttin machine before mixing w1ith the other ingre ients, so that the individual fibres are from one eighth to one quarter inch long.'

Certain other materials such as fluxes,

hardening agents, .release materials, plasticizing agents, pigments, or dyes, and the like, mayl of course be added in the wellunderstood manner, provided thati-they are of such nature as not to interfere with the desired and essential propertiesof the mixture. I'have found carnauba wax to be a satisfactory flux. It may be entirely omitted or usedin various quantities up to about 2%, depending u on the desired molding characteristics. Small amounts -of yhexamethylenetetramine may be employed, if desired,

v.as a hardening agent for the resin. 'While this is notnecessary, I have found that it serves to increase the heat-resisting qualities of the .final article, as well as its mechanical strength.

The proportions of the mixtures'may be varied' to a considerable extent according to thel degree of plasticity desired. One composition which I h ave found to give excellent results, both .in the laboratory and on a commercial scale, comprises:

Per cent by weight.

Reactive phenol resin (phase angle difference 0.66) 45 Ground mica (200 mesh screen) 5l Raw .silk (Chinese, unwashed) 3 Carnauba wax (flux) l l The behavior of molded samples having this composition is shown by curve (l) of the figure, as' hereinafter described.

In experimenting upon a large scale I have found that the .molding qualities of this mixture may ber improved by increasing the proportion of wax in the -above mixture to 2% and reducing the mica content to 50%. In

this event the phase difference may vary from about 038 to-about 045 at 350 meters wavelength, depending upon the time allowed in molding.

If it is desired to obtain a particularly heat-resisting product the -composition may be varied as follows:

The phase difference. of this mixture is approximately 0.7 at 350 meters, as, measured on the molded product.

Percent v I by weight. Reactive phenol resin (phase angle difference 0.66") 461/2 Mica (ground, 200 mesh) 461/2 -Hexamethylenetetramine 2 95 Silk (raw, Chinese) V3 Wax (carnauba, flux) 2 Anothertypical composition, in which the silk is replaced by cotton, is as follows:

Per cent v by weight. Reactive phenol resin (phase angle difference less than 1.0) 45 Ground mica 52. Dry white cotton 2 Carnauba wax l This mixture possesses a phasel difference of about 0.7 5 at 300 meters.

" rIypical compositions in which the fibrous -material is entirely dispensed with are the following Per cent by weight. Reactive phenol resin (phase yangle difference 0.66") 55 Ground 'mica (200.mesh); 45

having a phase difference of about 035 at 330 meters. v

Per cent I A by weight. Reactive phenol resin phase angle difference less than 1.0 f 'T5 -Powdered silica 25 having a phase digerence of about 088 at 300 meters, and y l l Phenol resin A bgegigg, sample of4 new hard rubber; and curve 3 in a Reactive phenol' resin (phase anglevdi typlcal sample of hard rubber two years old. ference less than L00) r 25 Compare Bureau of Standards, Technologie Powdered Silica 75 apel N0. 216, page 622). Hard rubber is having a phase diderence of about 0.95o at 300 meters.

I have also found that in some cases thefibrous material may itself constitute the inert, non-changing, liller. An example of such a composition is Per cent. (phase angle difference less than 1.0") 75 Raw Chinese-siiifilils-ii:: 25

having va phase diiference of about 0.930 at 300 meters.

In general, these mixtures flow well in the mold, cure in normal time, and yield molded articles of excellent mechanical strength, surface characteristics and permanence. These molded articles have a very low dielectric hysteresis as compared with known phenolresin molded articles, comparing favorably in this respect with hard rubber. As is Well known hard rubber tends to deteriorate in this respect with age and use, Whereas no such tendency has been observed with my novel A composition, which, in its preferredembodiments, is distinctly superior to old rubber, and closely approximates new rubber, as regards hysteresis losses.

Data regarding dielectric losses at various wave lengths between 200 and 1,600 meters are plotted in the accompanying diagram, wherein curve 1 indicates such losses in a certain molded product compounded in accordance with the first formula herein given, and measured in the molded sample according to the specifications of the American Society for Testing Materials, (vol. .Q3-part l, pages -827-840) the dielectric losses being expressed in terms of degrees phase difference, and also in percent power factor, the latter being the trigonometric sine of the phase difference angle. understood that material variations may occur, in the use of a particular molding mixture, according to the particular molding conditions, or after-curing employed which in turn is largely determined by the. size, shape and character of the molded piece.

As a rule a mixture compounded in accordance with this invention, and properly cured, should have a lphase difference not vexceeding about 1.0 degree in the vicinity of 300 meters (frequencies about 1,000 kilocycles) I have `found it possible to produce commercial molded products compounded in accordance with this invention which have a phase difference even lower than this figure, as, for example, the specimen from which curve 1 vwas plotted.

Curve 2 represents the dielectric losses over the same frequency range 1n a typlcal In this connection it will of course be phenolic resin compositions as heretofore made; and they are also far superior to hard -rubber `in respect to permanence.

The possession of this desirable property is of course of great advantage in numerous applications, particularly in the radio transmission and reception lields, as will readily be imderstood by those skilled in these arts. I have found the material particularly desirable for such uses as condenser parts, transformer parts, tube sockets and the like.

This application is a continuation of my co-pending application Serial No. 53,947 filed September 1, 1925.

I claim:

1. A molding mixture comprising a reactive phenol resin, and a iiller comprising mica and silk.

2.'A molding mixture comprising a reactive phenol resin, and a filler comprising mica and silk, the mica in finely powdered form and in predominating proportion by weight.

3. A molding Vmixture comprising a reactive phenol resin, and a filler comprising powdered mica, and silk containing the natural gums.

4. A molding mixture containing by Weight, powdered mica, forty to sixty parts; raw silk, two to eight parts; the balance consisting chiefly of a phenol resin of the reactive t e.

"'fyg. A molded article characterized by low dielectric hysteresis and comlpirising a hardened phenol resin, mica and si 6. A molding mixture comprising a reactive phenol resin having a phase angle difference-not exceeding 1.0-degree and a filler comprising mica and a fibrous material of high insulating value, the mica largely predominating.

7 A molding mixture comprising a reactive phenol resin having a phase angle difference not exceeding 1.0 degree and a. filler parts; said mixture yielding under standard vmolding conditions a molded product having the essential physical and mechanical characteristics of the hardened. phenol-resinoid products, and characterized by a phase difference not exceeding 1.0 degree.

' 8. A molding mixture comprising a reactive phenol resin and a iller comprising a' mineral substance of high insulating Value 10 and silk.

9. A molding mixture comprising a lowf hysteresis phenolic resin and a ller which is substantially non-reactive during the molding process, and which does not substantially increase the hysteresis loss in -the resulting molded product, said roduct being characterized by a phase di erence not exceeding about l".

ln testimony whereof I affix m si ature.

LWIS L. 

